Electric discharge device



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Inventors:

Geo-#ge F Murphg, Hcr'rvg C. Steinen bg www Thei'f Attov-neg.

i@ 8, 1935., G. F. MURPHY ET AL y ELECTRIC DISCHARGE DEVICE Filed Feb.25, 1951 Patented Oct. 8, 1935 UNITED STATES PATENT, OFFICE ELECTRICDISCHARGE DEVICE George F. Murphy, Schenectady, and Harry C.

Steiner, Scotia, N. Y., assignors to General Electric Company, acorporation of New York The present invention relates to electricaldischarge apparatus, more particularly to thermionic devices containingan ionizable medium and provided with a source of electrons, acooperating anode and an electrostatic control member or grid. Thepressure of the medium and the impressed voltages are such that adischarge of arc-like character is produced between the electrodes, theinitiation of the discharge being controlled by the voltage on the grid.Upon applying the anode voltage, the grid voltage determines whetherlthe arc will start 'and by a continued repetition of applying andwithdrawing the anode voltage the control member may determine theaverage plate current over a period of time. Devices of this character'have been described by A. W. Hull in an article entitled Hot cathodethyratrons in the G. E. Review, vol. 32, No. 2, April, 1929, pp. 213-223inclusive. Such devices find utility where large currents are to becontrolled with the application of very small amounts of energy to thegrid. Devices of this character often carry considerable current, and inorder to provide a sufficient number of electrons with which to producethe necessary ionization, cathodes of large size and weight must beemployed. Cathodes of the indirectly heated type are generally used forthis purpose on account of their extensive electron emitting surface andhigh operating eiiiciency. The matter of supporting these heavy cathodeswithin the envelope presents a diicult problem, particularly where largeleading-in conductors of suiicient current carrying capacity arerequired and these conductors provide the sole support for the cathode.The latter usually is positioned a considerable distance: from the stemin order not to heat the glass unduly, thus necessitating long supportleads which may cause a large amount of stress where they emerge fromthe stem. In certain cases the stems have been known to crack due tovibration or other movement of the cathode swinging at the end of theleading-in conductors. The movement of the cathode is not onlyundesirable from the standpoint of injury to the stem but also onaccount of the change in the spacing between the cathode and remainingelectrodes which deleteriously affects the operating characteristics ofthe device.

An object of the present invention is to improve on the supportingstructure of a cathode, particularly one of the indirectly heated typeto the end that a cathode of large bulk and Weight may be accurately andrigidly positioned Within the envelope. This object is attained in briefby relieving the leading-in conductors entirely of the support of thecathode so that these conductors are called upon only to deliverelectrical energy to the cathode. In our improved arrangement, thecathode is carried by arigid me- 5 tallic structure secured to theenvelope at a con- Venient place and the conductors are constituted offlexible wire. Another novel feature of our invention is an improvedform of end located at the anode stem which stem is characterized by alo double reentrant portion so as to protect the anode seal from damagedue to positive ion bombardment. Other objects and features will beapparent as the specication is perused in connection with theaccompanying drawing in 15 which Fig. 1 shows a view in elevation of theimproved tube; Fig. 2 is an enlarged View of the cathode shown in Fig. 1with a portion broken away and exposing the interior members, while Fig.3 is an enlarged cross sectional view of the 20 anode portion or theenvelope.

Referring to Fig. 1, numeral I designates the envelope ofan electricdischarge device which terminates in re-entrant stems 2 and 3. The lowerstem 3 is closed by a press 4, while theup- 25 per stem 2 carries atthecenter a small inverted tubular member 5 open at one end. About midwaybetween the inner end of the stem 2 and the place where it joins theenvelope, there is a transverse glass member 6 which carries a piece of30 tubing l closed at its upper end. 'Ihe member 'I is hermeticallysealed to a rigid conductor which passes, rather loosely, through thebore of the tube 5 and is secured to; an anode 9 of any suitable andwell known design. The rigid con- 35 ductor 8 is joined to a flexiblelead Il! for connection toexternal circuits. The grid or control membertakes the form of a perforated cylinder II closed at the lower end andsecured in position by embracing the stem 2 to which it is 40 clamped bya metal member I2'. A lead I3 is taken from the grid through a stem I4which closes the outer end of a transverse glass tubulature I5. In orderto improve the starting characteristics of the tube, metallic extensionsI6 are 45 afliXed to the lower end of the grid and these extensionscarrya starting ring I'I. The cathode I 8 consists of the usual form ofheater (not shown) of which only one of the conductors I9 isillustrated, and about this heater, suitably in- 0 sulated therefrom,are a plurality of rigidly spaced discs 20. These discs are usuallycoated with an electron emitting material such as barium carbonate(BaCOs) to produce an abundance of electrons necessary for carryingcurrent 55 through the tube. About the discs are located one or moreheat shields 2| perforated to allow the egress of electrons `and theingress of positive ions. The top of these shields is closed by acircular plate 22 which provides a support for one end of the enclosedheater (not shown). The lower end of the cathode is closed by three ormore heat shields 20' provided along their periphery with downturnedflanges which are secured to the interior surfaces of the respectiveheat shields 2 I. A cathode of this kind has been described in the Hullapplication Serial No. 487,- 533, filed October 9, 1930, and entitledCathode structures for thermionic devices. Also in the Pike applicationSerial No. 487,541, filed October 9, 1930, and entitled Cathodestructures for thermionic. devices. It is evident that the cathodeinvolves a considerable amount of metal and for this reason is quiteheavy, particularly in the larger size tubes. In order rigidly tosupport the cathode within the envelope and in accordance with ourinvention, we provide a rigid framework 23 consisting of U-shaped metalup'- rights which are secured, preferably by welding, to the surface ofthe outermost heat shield 2! and at the other end to a resilient band 24of metal. Three equidistantly arranged uprights are illustrated but itwill be understood that the number may vary, depending upon the weightand shape of the cathode to be supported. The member 24 is clamped aboutthe stem 3 and when this member is of suflicient length so as to obtaina large surface of contact with the stem, the framework is held rigidlyin place. Intermediate the positions of the cathode and clamp ring 24,there may be secured to the framework 23, two or more shields 25 inorder to protect the stem 3 from heat radiated through the lower end ofthe cathode. The current for the heater is conducted through a flexiblemulti-strand lead I9 connected to a solid leading-in conductor sealed inthe stem 4 and terminating in a ilexible lead 29. The other end (notshown) of the heater is attached to the cap member 22 so that thecathode or load current leads serve as a part of the heater circuit. Theload current is taken from the cathode by means of a pair of flexiblemulti-strand leads 26 connected in parallel, to flattened rigid rods 21sealed in the stem, also terminating in flexible leads 28 as in the caseof the heater circuit.

It is apparent that the heavy cathode structure which may weigh from onepound in the smaller size tubes to ten pounds or even more in thelargerI devices, is held rigidly in place by the framework and thestrain on the stern is reduced to a minimum by the improved method ofsupport. The fact that the leads. I9 and 26 are flexible, precludes anyof the cathode weight from being communicated to the rigid conductors2T, hence, precludes strain in the glass at the place where theconductors are sealed. It is also evident that the inverted tube 5prevents the arc discharge from bombarding the place where the conductor8 is sealed in the stem 'l and to that extent, also precludes punctureor cracking of the glass at this place.

An impro-ved structure of the type described finds particular utility inelectrostatically controlled arc discharge devices containing anionizable medium, such as inert gas or vapor. As stated hereinbefore,the pressure of the latter is such that an arc discharge capable ofcarrying large currents is produced and the starting of the arccontrolled by the inhibiting effect of the grid member IB. Alternatingcurrent is usually employed in the plate circuit so as to resto-re tothe grid in a` practical manner, the control function at the beginningof each complete cycle. It has been found during operation, that therigidity of cathode support offered by the framework 23 is such that thecathode is held strictly in proper position notwithstanding a relativelylong distance between the latter and the stem which supports it, and theelectrical characteristics of the tube as a whole are maintained uniformand reproducible. Moreover, due to the absence of glass strain at bothends of the envelope, the operating life of the tube is materiallyincreased.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. An electric discharge device comprising an envelope winch contains anionizable medium and which is closed by oppositely directed stems, ananode supported from one stem by means of a rigid leading-in conductor,a cathode supported from the other stem by a rigid framework, a exiblelead for the cathode, an extension formed on the anode-supporting stem,said extension terminating in a member which closely surrounds the anodeleading-in conductor and extends toward the anode-supporting stemwhereby said anode supporting stem is protected from positive ionbombardment.

2. An electric discharge device comprising an envelope terminating in astem, said envelope containing an ionizable medium and a plurality ofelectrodes, one o-f said electrodes supported from said ste-m by meansofa conductor, an extension formed on the stem, said extension terminatingin a member which surrounds said conductor and extends toward said stem,the electrode to which said conductor is secured being mounted whollyexterior to said extension.

3. An electric discharge device comprising an envelope terminating in astem, said envelope containing an ionizable medium and a plurality ofelectrodes including an anode, said anode supported from said stem bymeans of a conductor, an extension formed on the stem, said extensionterminating in a member which surrounds the anode conductor only andextends toward said stem.

4. An electric discharge device comprising an envelope which contains anionizable medium and which is closed by oppositely directed stems, ananode supported from one stem by means of a conductor, a cathodesupported from the other stem, an extension formed on the anodesupporting stem., said extension terminating in a member which surroundsthe anode conductor and extends away from the anode and cathode.

GEORGE F'. MURPHY. HARRY C. STEINER.

